1. Field of the Invention
The present invention relates generally to a library apparatus, and more specifically to a library apparatus which can prevent damage to a flat cable connected to an accessor robot of the library apparatus.
2. Description of the Related Art
Known library apparatus have a plurality of cells for storing cartridges that accommodate information storage media such as magnetic tape cartridges and optical disk cartridges. A cartridge stored in a cell, selected from a plurality of cells, is loaded to a drive unit within the library apparatus. The drive unit executes a process, for example performs a read or write operation, using the medium loaded into the cartridge.
To load and unload the cartridge, the library apparatus is generally provided with a cartridge access station. Moreover, the library apparatus includes an accessor robot to transfer the cartridge between the cartridge access station, each cell, and the drive unit. To effectively transfer cartridges in a large sized library apparatus, the accessor robot moves along at least one straight line, for example in the horizontal direction. In the commonly invented Japanese Published Unexamined Patent Application HEI 8-235729, for example, the accessor robot moves with a driving force of its own motor along a straight rail provided in a horizontal direction.
To supply the electrical power to the accessor robot and exchange control signals, the accessor robot is connected to a flat cable. One end of the flat cable is fixed to the accessor robot and the other end is fixed to a housing of the library apparatus. The flat cable accommodates a moving range of the accessor robot which exceeds 20 m in the case of a large sized library apparatus. To prevent slackness in the flat cable, it is important to keep tension on the cable during the range of motion of the accessor robot.
The flat cable winds around a cable drum, and an arm supports the cable drum to allow the drum to rotate. At least one idler pulley is attached to the arm and a wire rope winds around the idler pulley to give constant tension to the flat cable irrespective of a moving position of the accessor robot, to prevent looseness in the cable. One end of the wire rope is fixed to a housing of the library apparatus, and the other end is connected to the accessor robot. When the accessor robot moves a certain distance, the idler pulley moves about half that distance. Accordingly, the cable remains under constant tension by winding the flat cable on the cable drum which moves together with the idler pulley which is connected to the wire rope.
A problem occurs in that the flat cable moves with the accessor robot and the cable may become mechanically damaged during the movement. For example, when the power feeding mechanism including the pulley and cable drum mentioned above is employed, the flat cable may be damaged due to the friction between the cable drum and flat cable. When the cable is damaged, electrical power and control signals that are otherwise supplied to the accessor robot via the flat cable cease being supplied.
One particular instance of damage occurs with the cable drum that includes a pair of flanges provided at both ends of a cylindrical portion of the drum. Since the flanges have a diameter larger than the cylindrical portion of the drum on which the flat cable is wound, the flat cable can rub upon the flanges or ride on the flanges during the operation of the accessor robot, and thereby damage an edge of the flat cable. Such a problem results when a center of the cable drum deviates from a center of the flat cable due to inaccuracies during assembly. Since the accessor robot and cable drum move independently, if the cable drum center deviates from the flat cable center, the wire rope that applies tension to the flat cable causes the flat cable to deviate toward the flange of the cable drum.
Moreover, even when the flat cable is centered with respect to the drum, the manufacturing accuracy along the width of the linear moving flat cable is about 3 cm per 10 m of linear movement. Thus, both sides of the flat cable generate different tensions even when the flat cable is extended in a straight line, causing the flat cable to deviate toward a flange of the cable drum. Due to the repetitive operation of the accessor robot, the edge of the flat cable may be damaged by contacting against the flange of the drum.
Therefore, it is an object of the present invention to provide an improved library apparatus which can prevent damage to a flat cable connected to an accessor robot of the library apparatus. Other objects of the present invention will become apparent from the following description.
The above objects are met or exceeded by the present invention. According to a first aspect of the present invention, a library apparatus is provided which includes a cell unit having a plurality of cells which provide cartridges. The cartridges accommodate storage media. A drive unit executes processes using the storage media, and an accessor robot transfers a cartridge between the cell units and the drive unit. A flat cable has a first end and a second end with the first end being fixed to a reference position, and a connecting mechanism connecting the second end of the flat cable to the accessor robot. The flat cable is wound around a cable drum, and an arm supports the cable drum to allow the drum to rotate. A wire rope and the arm are arranged to provide tension to the flat cable.
The connecting mechanism is provided with a first metal plate to which the second end of the flat cable is fixed, a second metal plate for supporting the first metal plate to rotate, and a third metal plate for supporting the second metal plate to slide in the direction perpendicular to the longitudinal direction of the flat cable. According to this structure, since the connecting mechanism of the particular structure is employed, a center of the flat cable may be matched with a center of the cable drum to prevent damage to the flat cable.
According to a second aspect of the present invention, the cable drum has a pair of flanges at both ends, and a pair of cable guides are provided between the flanges and the flat cable. The cable guide is employed to match the flat cable center with the cable drum center, to prevent damage to the flat cable.
According to a third aspect of the present invention, the cable drum is constructed of first and second portions in a direction of the rotating shaft, and the first and second portions include symmetrical spiral grooves. The spiral grooves of the cable drum provide a force that causes the flat cable center to be matched with the cable drum center, and therefore damage of the flat cable can be prevented.
According to a fourth aspect of the present invention, the cable drum has a generally convex drum shape to provide a force that matches the flat cable center to the cable drum center due to the rotation of the cable drum. Thus, damage to the flat cable can be prevented.
According to a fifth aspect of the present invention, an outer surface of the cable drum has a plurality of grooves parallel to the rotating shaft. The plurality of grooves reduce a force that causes the flat cable to move toward the end of the cable drum when the cable drum rotates, and thereby prevents damage of the flat cable.
According to a sixth aspect of the present invention, the outer surface of the cable drum has a sufficiently small friction coefficient due to polishing by buffing or by applying a low friction polytetrafluoroethylene (PIFE) coating, commonly known as a TEFLON(copyright) coating, to the drum. Since the outer surface of the cable drum has a sufficiently small friction coefficient, there is a reduction in the force that causes the flat cable to move toward the end of the cable drum when the cable drum rotates, and damage of the flat cable can be prevented.
According to a seventh aspect of the present invention, the library apparatus provides a grounded conductive brush that is electrically connected to the cable drum to eliminate static electricity from the cable drum. According to this structure, since static electricity generated by contact between the flat cable and cable drum can be eliminated, friction by static electricity is alleviated. Thus, damage to the flat cable is prevented by using the same principle as that described in the sixth aspect of the present invention, i.e., reducing the friction coefficient of the cable drum.